1. Field of the Invention
This invention is concerned with the product obtained by reacting a borated alkyl catechol with certain monoalkylamines and the use of said product in lubricant compositions.
2. Description of the Relevant Art
Wear and deposits limit the useful life of automobile and truck engines.
Thus, there is a great need to find lubricants that reduce the oxidation, wear and deposits in the engine, thus increasing the lifetime of the engine.
U.S. Pat. No. 2,795,548 discloses the use of lubricating oil compositions containing a borated alkyl catechol. The oil compositions are useful in the crankcase of an internal combustion engine in order to reduce oxidation of the oil and corrosion of the metal parts of the engine.
There is a problem with the use of borated alkyl catechols in lubricating oils since they are sensitive to moisture and hydrolyze readily. The hydrolysis leads to haze and/or precipitate formation which must be filtered out prior to use. It has now been found that the borated alkyl catechols may be stabilized against hydrolysis by complexing the borated alkyl catechol with certain monoalkylamines.
More importantly, lubricating the crankcase of an internal combustion engine with a lubricating oil containing the reaction product of a borated alkyl catechol and certain monoalkylamines reduce oxidation and wear in gasoline engines and deposits in diesel engines.
U.S. Pat. No. 2,497,521 to Trautman relates to the use of amine salts of boro-diol complexes in hydrocarbon oil compositions. The amine salts of the boro-diol complexes are useful as stabilizing agents, i.e., antioxidants. The described boro-diol complexes include diols selected from the group consisting of glycols and polyhydroxy benzenes, including catechol. Catechol is a small polar compound which has poor solubility in essentially non-polar base oils under ambient conditions. The use of long chain alkyl groups on the alkyl catechols to enhance its solubility and compatibility in a base oil is not taught in Trautman. A wide range of amines to prepare the salts is taught; indeed "any organic amine may be employed" (Col. 3, lines 51-71).
A recent patent (U.S. Pat. No. 4,328,113) assigned to Mobil Oil Corporation teaches the use of high molecular weight (C-8+) amines and diamines with boric acid itself for use as grease and lubricating oil additives. The use of borated catechols let alone borated alkylated catechols is not taught in this patent.
U.S. Pat. No. 4,655,948 to Doner et al. discloses grease compositions having increased dropping points. Among the compositions described are mixtures of a hydroxy-containing thickener and borated catechol compounds having the structure: ##STR1## where R.sub.1 and R.sub.2 are each H or C.sub.1 to C.sub.40 ; and where R.sub.3 is a C.sub.1 to C.sub.40 hydrocarbyl and can contain, additionally, oxygen, sulfur and/or nitrogen-containing moieties.
The catechol amine borate compounds of Doner et al., as indicated in the above formula, are described as trigonal boron compounds having nitrogen-boron single bonds formed by driving the condensation reaction to completion via the azeotropic removal of water. A variety of useful amines are described in Col. 2 lines 62, et seq. Although some amines listed contain secondary amine structures, the common link in all amines is the presence of primary amine structures. It is also to be noted that Doner's list of amines are all high molecular weight aliphatic amines, e.g., oleyl amine or are aromatic, i.e., aniline. Primary amines such as monoalkylamines with short alkyl chains are not specifically described.
U.S. Pat. Nos. 3,133,800 and 3,203,971 to De Gray et al. disclose glycol borate amine compounds of aliphatic saturated glycols, useful as fuel additives, for example as deicing agents and bacteriocides. Useful amines, among others, include those with alkyl groups having from 3 to 20 carbon atoms.
U.S. Pat. No. 2,883,412 to Lowe discloses p-xylylene diamine salts of glycol boric acids having superior corrosion inhibiting properties. Among the compounds disclosed are p-xylylene diamine adducts of alkyl catechol borates, such as derived from butyl and cetyl catechol (Col. 3 lines 61-68).
Reactions of trialkyl borates with amines, including diethylamine, triethylamine, cyclohexylamine, and ethylenediamine are described by Wilson in J. Chem. Soc. Dalton, 1973, pp. 1628 and by Colclough et al. in J. Chem. Soc., 1955, pp. 907. The latter, in addition, describes reactions of triphenylborates with amines and on p. 909 shows that attempts to prepare a diethylamine product resulted in a product that was low in amine content, but dry ethylamine formed complex with triphenylborate. Moreover, even the much more stable pyridine complex of triphenylborate described in this paper hydrolyzed completely in moist air in 5 days. These references do not mention alkyl catechol derivatives.
However, Kuremel et al. in J. Amer. Chem. Soc. 78, pp. 4572 (1956) does talk about catechol-boric acid-pyridine complexes. Kuremel shows on p. 4574 that "there is complete dissociation of the complexes into their substituents (pyrocatechol, pyridine, and boric acid) in alcoholic solution". Alkyl catechols were not mentioned.
U.S. Pat. No. 4,629,578 to T. V. Liston teaches that a complex of borated alkyl catechol with a succinimide is useful in lubricant compositions. The succinimide additives of Liston are effective in stabilizing the borated alkyl catechols to hydrolysis. Preferred succinimides have a number average molecular weight of about 600 to about 1,500 (Column 4, lines 12, et seq.). These high molecular weight succinimides effectively dilute the concentration of the desired borated alkyl catechols. In addition, using high molecular weight succinimides for hydrolytic stabilization results in higher transportation costs for the additive, and a loss of flexibility since their use is limited to formulations containing succinimides as dispersants, due to compatibility problems.
Previously, it was believed that low molecular weight amines would not be useful in lubricants subjected to high temperatures, e.g., &gt;100.degree. C. because of the volatility of the amines; that is, it was believed that the amines would be lost during use and not provide ongoing stabilization against hydrolysis. Indeed, all prior art examples show lubricant-type compositions with higher molecular weight amines than the monoalkylamines of this invention.
We have now surprisingly found that certain monoalkylamine-borated alkyl catechol complexes are stable with respect to decomposition to starting materials under "in use" conditions. The certain monoalkylamine stabilized alkyl borated catechols of this invention passed the L-38 engine test (with a score of about 30 mg weight loss), where the presence of "free" amine such as oleyl amine under these conditions would give very high (300-600 mg) weight losses due to corrosion of the copper and lead bearings. Also, calorimetry data (DSC) shows that the monoalkylamine stabilized alkyl borated catechols of this invention are stable to about 200.degree. C., which is significantly above the sump temperature of a gasoline engine.
The thermal stability of catechol boron amine complexes is not predictable. For example, dimethylamine does not form a stable complex with alkylated borated catechols nor does diisopropyl amine. The interaction of steric effects, nitrogen basicity and boron electrophilicity all come into play. These factors affect the equilibrium between the reactants and the products and make predictions of thermal stability impossible. One also cannot predict hydrolytic stability, which may or may not be related to thermal stability.
The problem, therefore, addressed and solved by this invention is how to hydrolytically stabilize borated alkyl catechols so as to achieve a higher concentration of boron per pound of the borated alkyl catechols. This is achieved by complexing such catechols and stabilizing the same with a low molecular weight stabilizing material, i.e., certain monoalkylamines.